The present invention relates to a device for regulating the idling rpm of an internal combustion engine having an intake pipe with a throttle valve disposed therein, which valve can be actuated as desired. Around the throttle valve extends a bypass having a bypass valve which can be controlled as a function of operating parameters of the internal combustion engine, said bypass valve having a valve element which is displaceable relative to a valve seat by an electromagnet so as to regulate the size of a passage cross section, said valve element having a pressure-equalization surface in a back-pressure chamber from which a pressure-equalization connection leads to the intake side of the valve element.
Devices of this type serve to keep the content of noxious substances in the exhaust gases of internal combustion engines low and to decrease the fuel consumption. They are at present finding wider and wider use. As example of the state of the art, mention may be made of Federal Republic of Germany OS 31 13 986. In both of them it is specifically stated that the valve element is to be pressure equalized. This is also to be definitely striven for so that a valve positioning element can be displaced with as little force as possible and remains by itself in the position in which it is. In accordance with Federal Republic of Germany OS 30 10 167, the pressure-equalization connection is a borehole which extends through the valve element. In Federal Republic of Germany OS 31 13 986 it is a conduit which debouches between the bypass valve and the intake pipe into a line leading to the bypass valve.
It has been found that the force which moves the valve element in its opening direction is dependent not only on the pressure difference but also on the position of the valve element. This is due in particular to the conditions of flow in the bypass valve, which change with the position of the valve element. Therefore in the known devices only incomplete pressure equalization of the valve element of the bypass valve is possible.